Technological advances in computer hardware, software and networking have lead to efficient, cost effective computing systems (e.g., desktop computers, laptops, handhelds, cellular telephones, servers, . . . ) that can communicate with each other from essentially anywhere in the world in order to exchange information. These systems continue to evolve into more reliable, robust and user-friendly systems. Furthermore, these systems allow locating people, equipment, and other tangibles. Such systems are further employed in providing directions (e.g., driving directions) and/or maps, controlling access to restricted areas, monitoring inventory (e.g., theft prevention), and the like.
A number of location sensing technologies are commonly available. Examples of location sensing systems can include, Active Badges, Active Bats, MotionStar, VHF Omni-directional ranging, Cricket, MSR radar, Easy Living, Smart Floor, and Global Positioning System (GPS). Each one of these systems has its respective limitations. For example, location techniques that employ satellite based GPS signals for range measurements, lack signal availability in covered in-door environments where line of sight to the satellites is not available.
Another type of location sensing technology is radio-based. Radio-based location systems typically utilize a database of radio base station locations. One can determine the location of a receiver by analyzing the signal received and having prior knowledge of the location of the source of those signals. For example, a mobile radio can detect some of these base stations, and a triangulation routine can be invoked to estimate a location of the mobile radio as a function of known locations of the detected base stations. Knowledge of the signal source location plays an important role in such systems.
Moreover, disparate types of radio base stations have been employed in such systems including, for instance, Wi-Fi (e.g., 802.11), cellular, FM radio, AM radio, TV station, and the like. However, the database of base stations can be incomplete or become out of date as base stations are moved, removed, and added. Such problem poses critical challenges for Wi-Fi, since these base stations are easy to buy, install, and/or reinstall in a new location.
The radio source location can be determined by using a radio surveillance process, where the signals are first collected and subsequently analyzed to compute the signal source location. For example, a conventional technique utilized to determine source locations, and updating of the database of base stations can be wardriving. Wardriving involves searching for Wi-Fi wireless networks by a moving vehicle. For example, a wardriver can employ a Wi-Fi equipped computer (e.g., laptop, personal digital assistant, and the like) to detect the networks (e.g., wireless access points, base stations). Moreover, a GPS can measure and log locations of the network as a car or truck traverses within a geographic region.
Accordingly, a mobile receiver records received signals during motion, while at the same time periodically recording a respective location, as determined by devices such as the GPS receiver. A frequency range can then be scanned linearly, while incoming packets of data related to the received signal are recorded as they arrive. The collected data is then analyzed to estimate the position of the radio source.
The limited frequency scanning rate that pertains to such approach can cause short duration signals to be missed. Put differently, incoming signals that have a short detection period are not properly identified by the linear scan of the frequency spectrum. Moreover, periodic location assessment can cause received signals to be falsely grouped together at places where the location information was received. Additionally, any delay in the processing pipeline can further introduce errors in the true location of the received and recorded signals. Employing faster equipment to increase resolution and expedite processing can somewhat mitigate these problems, however associated costs will substantially increase.